Known ringer components often control a piezoelectric crystal transducer, which because of its high impedance and good acoustical efficiency assures good line adaptation to the impedance of the calling alternating voltage generator in the switching center. However, they do not have an adequate voltage supply for a microcontroller, which would enable flexible and comprehensive functional and operational convenience in terms of ringing tone detection and tone production.
If the ringing tone transmission is carried out through a low-impedance loudspeaker, then the high-impedance output stage of the calling alternating voltage generator must be adapted to the low-impedance loudspeaker with the aid of a transformer. In the speech mode, when the loudspeaker is to be driven by the reception path, the transformer must usually be switched off and the loudspeaker coupled directly to the amplifier. Versions with two loudspeakers of different impedance are also known.
In order not to incur such additional expense, versions are described, for instance in German Published, Non-Prosecuted Application DE 41 13 113 A, that have a direct current converter, which in the ringing tone mode converts the high impedance into a lower impedance at a correspondingly reduced voltage, and thus enables the voltage supply for operating a microcontroller as well. The attainable efficiencies of the direct voltage converter are approximately 70%. However, the power furnished to the acoustic transducer may drop below satisfactory values under some circumstances.